Welcome! Today, we will explore creating a simple address book application using Java's HashMap. This task will help you understand how to manipulate a HashMap in Java, focusing on adding, retrieving, and deleting entries. By the end of this lesson, you'll have a solid grasp of these fundamental operations.

In this task, we will implement three methods to manage our address book:

• addContact(String phoneNumber, String name): Adds a new contact. Returns false if the contact already exists; otherwise, it adds the contact and returns true. For this task, let's assume names do not change, so it's not allowed to overwrite an existing contact's name.
• getContact(String phoneNumber): Retrieves the name for a given phoneNumber. Returns null if the contact does not exist.
• deleteContact(String phoneNumber): Deletes a contact with the given phoneNumber. Returns true if the contact exists and is deleted, otherwise.